1. Field of the Invention
The present invention relates to polysulfone based polymer, a polymer electrolyte membrane comprising the polymer, a membrane-electrode assembly comprising the membrane, a fuel cell comprising the membrane, and a method for preparing the polymer, particularly to polysulfone based polymer with novel structure, a polymer electrolyte membrane comprising the polymer, a membrane-electrode assembly comprising the membrane, a fuel cell comprising the membrane, and a method for preparing the polymer.
2. Description of the Related Art
A fuel cell can be classified into PEMFC (polymer electrolyte membrane fuel cell), PAFC (phosphoric acid fuel cell), MCFC (molten carbonate fuel cell), SOFC (solid oxide fuel cell), etc. depending on the kinds of electrolyte, and the operation temperature and material quality of components of the fuel cell are varied depending on the kinds of electrolyte.
PEMFC (Polymer Electrolyte Membrane Fuel Cell) can exhibit excellent output, low operation temperature and rapid response properties, compared to other fuel cells.
A fuel cell may contain an electricity generation part where electricity is generated, a reformer, a fuel tank and a fuel pump, etc. The electricity generation part forms a body of the fuel cell, and the fuel pump supplies fuel in the fuel tank to the reformer. Hydrogen gas is generated through the reformer, and fuel is supplied to the electricity generation part by the pump to generate electrical energy by electrochemical reaction. The electricity generation part may include a membrane electrode assembly (MEA) which contains anode, cathode and a polymer electrolyte membrane components.
Fuel cells also can be classified as fuel direct supply or internal reforming fuel cell depending on the fuel supplying method, and DMFC (direct methanol fuel cell) is representative of a fuel direct supply fuel cell.
Since the direct methanol fuel cell uses a polymer electrolyte membrane as electrolyte, it can be classified as a polymer electrolyte type fuel cell.
The direct methanol fuel cell does not use hydrogen reformer, etc. because it employs methanol as fuel It can be operated at low temperature, and thus it can provide a simple and compact system suitable for electric power of small devices and portables.
Electricity generation in the direct methanol fuel cell can be provided as follows: Methanol is supplied to the anode electrode and decomposed into proton, electron and CO2 by oxidation reaction of electrode catalyst, and proton is transferred to cathode through the polymer electrolyte membrane and electron is transferred to cathode through external circuit. In the cathode, oxygen flowing from the air, electron transferred through the external circuit, and proton transfers through the membrane react to produce water. The electrochemical reaction is represented by the following Reaction Formula 1:Anode: CH3OH+H2O→CO2+6H++6e−Cathode: 3/2O2+6H++6e−→3H2OTotal reaction: CH3OH+ 3/2O2→CO2+2H2O  <Reaction Formula 1>
As the electrolyte membrane of the polymer electrolyte type fuel cell, a functional proton exchange membrane capable of cation exchange can be used. In commercial applications, a proton exchange membrane comprising sulfonic acid group is frequently employed. Sulfonic acid is strongly acidic and the C—S bond is stable even under oxidation conditions. In order to maintain proton conductivity high in the proton exchange membrane comprising sulfonic acid functionality, water molecules also should be present. In the presence of water molecules, a sulfonic acid functionality existing in the electrolyte membrane is dissociated into sulfonate anion and proton, and the proton is transferred by proton concentration gradient or electric field as in sulfuric acid solution electrolyte. Proton conductivity can be influenced by the number of sulfonic acid groups present in the polymer electrolyte membrane, structure of the polymer electrolyte membrane, and the amount of water contained in the polymer electrolyte membrane, etc.
A typical current polymer electrolyte type fuel cell is a fluorine containing polymer electrolyte membrane such as Nafion membrane, Aciplex membrane, Flemion membrane or Dow membrane. The fluorine containing polymer electrolyte membranes has deteriorated proton conductivity at high temperature of 100□ or more, high fuel gas permeability, and is expensive. And, as proton conductivity increases, water permeability of the polymer electrolyte membrane increases, thereby increasing permeability of fuel (for example, methanol). Thus, it is difficult to simultaneously have high proton conductivity and low fuel permeability.
Accordingly, there is a demand for improved polymer electrolyte membranes, particularly polymer electrolyte membranes having low preparation cost, high proton conductivity, and/or low fuel permeability.
The above information dclose din this Background section is only for the enhancement of understanding of the background of the invention and therefore it may contain information that does not form prior art that is already known.